Rare earth perfluorotertiarybutoxides containing coordinated ammonia

ABSTRACT

RARE EARTH PERFLUOROTERTIARYBUTOXIDES CONTAINING COORDINATED AMMOIA AND HAVING THE FORMULA   (NH3)3M(OC(CF3)3)3   WHEREIN M REPRESENTS AN ION OF A RARE EARTH METAL, ARE PREPARED BY REACTING PREFLUOROTERTIARYBUTANOL WITH AN IONIZABLE RARE EARTH SALT AND AMMONIA IN THE PRESENCE OF AN INERT SOLVENT. THESE COMPOUNDS ARE NOVEL AND MORE VOLATILE THAN ANY RARE EARTH COMPOUNDS PREVIOUSLY KNOWN. BECAUSE OF THEIR VOLATILITY, THE COMPOUNDS ARE USEFUL IN SUCH APPLICATIONS AS THE SEPARATION OF INDIVIDUAL RARE EARTHS BY FRACTIONAL SUBLIMATION.

United States Patent O 3,631,081 RARE EARTH PERFLUOROTERTIARYBUTOXIDES CONTAINING COORDENATED AMMONIA Dale K. Huggins, Convent Station, and William B. Fox,

Morristown, N..l., assignors to Allied Chemical Corporation, New York, N.Y. No Drawing. Filed Jan. 19, 1970, Ser. No. 4,133 Int. C1. C07] /00 US. Cl. 260-429 R 10 Claims ABSTRACT OF THE DISCLOSURE Rare earth perfiuorotertiarybutoxides containing coordinated ammonia and having the formula wherein M represents an ion of a rare earth metal, are prepared by reacting prefluorotertiarybutanol with an ionizable rare earth salt and ammonia in the presence of an inert solvent. These compounds are novel and more volatile than any rare earth compounds previously known. Because of their volatility, the compounds are useful in such applications as the separation of individual rare earths by fractional sublimation.

BACKGROUND OF THE INVENTION This invention relates to rare earth perfluorotertiarybutoxides containing coordinated ammonia and to a method for their preparation.

Efforts have been made in recent years by independent teams of researchers to develop volatile compounds of rare earth metals. One potential application of these compounds would be in processes for separating the individual rare earth elements. Because the rare earths are very similar chemically, especially with respect to their salts, which tend to form mixed crystals and solid solutions, they are very difiicult to separate. A typical present commercial method uses solutions of expensive reagents to elute the rare earths from ion exchange columns. In addition to being costly, this method is also quite slow.

The vapor-phase separation of rare earths by fractional sublimation and gas chromatography has been accomplished using rare earth tris chelates of p-diketones, such as 2,2,6,6-tetramethyl 3,5 heptanedione. These chelates were the most volatile rare earth compounds known prior to our invention. For example, the ytterbium tris chelate of 2,2,6,6 tetramethyl 3,5 heptanedionesublimes at a moderate rate at a pressure of about 0.08 mm. Hg and at a temperature of 115 to 120 C.

The novel compounds of this invention are rare earth perefluorotertiarybutoxides. Rare earth hydrocarbon alkoxides are known compounds; however, they are either nonvolatile or they volatilize with great diificulty. For example, the most volatile of these compounds, the isopropoxides and tertiarybutoxides, require temperatures of 200 to 300 C. and pressures of 0.1 to 0.0001 mm. Hg in order for sublimation to occur.

It is an object of this invention to provide novel, highly volatile compounds of the rare earth elements.

SUMMARY OF THE INVENTION This invention provides novel rare earth compounds which are more volatile than any rare earti compounds previously known. These novel compounds are rare earth perfiuorotertiarybutoxides containing coordinated ammo nia, and having the formula (NH M[OC(CF wherein M represents an ion of a rare earth metal. As used herein and in the appended claims, the term rare earth refers to the elements scandiurn, yttrium, and the elements having atomic numbers 57 through 71 inclusive.

3,631,081 Patented Dec. 28, 1971 The compounds of this invention are prepared by reacting, under substanutially anhydrous conditions, perfluorotertiarybutanol with an ionizable rare earth salt and ammonia in the presenne of an inert solvent, as represented by the following equation:

wherein M represents an ion of a rare earth metal and X represents an anion forming an ionizable salt with the rare earth metal. This result is entirely unexpected in view of the prior art. It is known that when ionizable salts of other metals react with an alcohol in the presence of excess ammonia to produce metal alkoxides, the metal alkoxides obtained are free of coordinated ammonia. At least two attempts to prepare rare earth hydrocarbon alkoxides by this method have been reported, and these attempts were both unsuccessful. See K. S. Mazdiyasni et al., The Preparation and Some Properties of Yttrium, Dysprosium, and Ytterbium Alkoxides, in Inorganic Chemistry, 5, pp. 342-346 (1966), and D. C. Bradley, Preparative Inorganic lReactions, vol. 2, ed. by W. L. Jolly, Interscience-Wiley, New York, 1965', pp. 174-177. The latter reference, at page 175, indicates that a stable, insoluble ammoniate is obtained instead of the alkoxide. Prior to our invention, such ammoniates were the only compounds of the rare earth elements known to contain coordinated ammonia; and, unlike the compounds of this invention, these ammoniates are wholly inorganic.

The process of this invention is conveniently carried out at room temperature and atmospheric pressure. At these conditions the ammonia is present as a gas and forms an atmosphere over the remainder of the reaction mixture. The reaction proceeds readily at these conditions, but temperatures departing from room temperature and pressures departing from atmospheric pressure can be used if desired. The upper temperature limit is determined by the thermal stability if the reactants and products, and is about 250 C. The lower temperature limit is that at which the reaction rate becomes impractically slow, and is about C. The upper pressure limit is determined simply by the strength of the reaction vessel employed. Pressures below atmospheric can be employed provided at least a stoichiometric amount of ammonia is present.

It is preferable to use at least a stoichiometric amount, based on the rare earth salt, of perfluorotertiarybutanol in the reaction in order to avoid product containing the anion of the salt. It is also preferable to use at least a stoichiometric amount of ammonia in order to drive the reaction toward completion. Generally, it is preferable to use an excess of both of these reactants. I

The halides and sulfates of the rare earth metals are representative of the ionizable rare earth salts which can be used in the process of this invention. The trichlorides are preferred. Particularly good results are obtained using the trichlorides of yttrium and the elements of the lanthanum series, i.e., the elements having atomic numbers 57 through 71.

Most common organic solvents are suitable as the inert solvent employed in the reaction, including benzene, chloroform, cyclohexane, ligroin, tetrahydrofuran, acetonitrile, ether and methylenedichloride.

Because of their high volatility, the compounds of this invention are useful in many applications. As previously indicated herein, one application of these compounds is in processes for separating the individual rare earth elements. Separation can be effected by either fractional sublimation or gas chromatography in accordance with methods known in the art. For example, separation by fractional sublimation is achieved by introducing mixtures of the compounds of this invention into a vacuum sublimator, such as developed by Berg and Hartlage and described in Anal. Chim. Acta, 33, pp. 175-181 r1965). The volatilized compounds are moved through the sublimator with an inert gas, such as nitrogen or helium, as carrier. Contact of the vapor with the walls of the sublimator results in selective condensation of the compounds. The thermal gradient in the sublimator preferably ranges from about 130 C. in the hottest zone to about C. at the coldest end. Separation by gas chromatography is achieved by introducing mixtures of the compounds into a column having, typically, an inside diameter of 2 to 4 mm. and a length of 10 to 100 cm., and constructed of an inert, nonmetallic material, such as glass or polytetrafluoroethylene. The column is packed with a convenial solid support, such as diatomaceous earth, and a liquid phase such as a silicone polymer leg, General Electric Co. SE-) or a hydrocarbon (e.g., Apiezon grease L. M, N, or T). The column and inlet port temperatures are preferably in the range of 100 to 200 C.. and the separation is effected in the substantial absence of moisture and oxygen.

When subjected to controlled hydrolysis, the components of this invention produce extremely pure and reactive powders of rare earth oxides.

Other potential applications of the compounds of this invention include their use as catalysts in homogeneous gas phase reactions, and as the lasing component in gaseous lasers.

The following examples further illustrate the invention. In each of the examples, the product was identified by elemental and infrared spectrum analyses.

EXAMPLE 1 The entire preparation was performed under ubstantially anhydrous conditions. Into a 3 neck. 100 ml.. round bottom distilling flask were placed 3.91 grams of anhydrous ytterbium trichloride. Using vacuum techniques, ml. of diethyl ether and 10.0 grams of perfluorotertiarybutanol were condensed into the flask at 80 C. The contents of the flask were warmed to room temperature and then stirred as gaseous ammonia was slowly added until the pressure in the flask remained constant at one atmosphere. White solids (Nl-i Cl) formed during the addition of ammonia. After the solids had settled. the clear mother liquor was decanted. Ether was evaporated from the liquor under vacuum, leaving the crude product as white solids. The crude product was purified by being sublimed twice at 0.1 mm. Hg and 85 C. The purified product was identified as (NH YhlOCtCF EXAMPLE 2 The procedure of Example 1 was followed except the reactants were 6.93 grams of anhydrous lanthanum trichloride and 20.0 grams of perfluorotertiarybutanol, and the solvent consisted of 100 ml. of methylenedichloride. The product was identified as (NH La| OCtCF EXAMPLE 3 The procedure of Example 1 was followed except the materials used were 3.72 grams of gadolinium trichloride. 10.0 grams of perfluorotertiarybutanol, and 100 ml. of diethyl ether, and the product was sublimed twice at 100 C. The product was identified as 3)3 l l s s i3 EXAIVIPLE 4 The procedure of Example 1 was followed. except the materials used were 2.76 grams of yttrium trichloride. 10.0 grams of perfluorotertiarybutanol. and 100 ml. ot diethyl ether, and the reaction product was sublimed twice at 105 C. The product was identified as 4 EXAMPLE 5 A comparison of the relative volatilities of the compounds of the present invention with the rare-earth complexes of 2.2,6.6-tetramethyl-3,5-heptanedione (previously regarded as the most volatile rare-earth compounds) was made by determining the temperature required to give similar rates of sublimation of comparable complexes. A sublimator containing Yb[OC(CF (NH and another containing the tris-2,2,6,6-tetramethyl-3,5-heptanedione chelate of ytterbium [Yb(thd) were attached to the same vacuum line and the compounds were sublimed simultaneously. The minimum temperature required for a perceptible rate of sublimation was to C. for Yb[OC(CF (l lI-l and to C. for Yb(thd) The lower required temperature demonstrates the greater \olatility of the compounds of this invention.

We claim:

1. Rare earth perfiuorotertiarybutoxides containing coordinated ammonia and having the formula wherein M represents an ion of a rare earth metal.

2. The rare earth perfluorotertiarybutoxides of claim 1 wherein the rare earth metal is selected from the group consisting of yttrium and the elements having atomic numbers 57 through 71 inclusive.

3. The rare earth perfluorotertiary-butoxides of claim 1 wherein the rare earth metal is selected from the group consisting of yttrium, lanthanum, gadolinium and ytterbium.

4. A process for preparing rare earth perfluorotertiarybutoxides containing coordinated ammonia and having the formula (NH M[OC(CF wherein M represents an ion of a rare earth metal, which process comprises reacting, under substantially anhydrous conditions, perfluorotertiarybutanol with an ionizable rare earth salt and ammonia in the presence of an inert solvent.

5. The process of claim 4 wherein the amount of ammonia employed is in excess of the stoichiometric amount required based on the rare earth salt.

6. The process of claim 5 wherein the amount of perfluorotertiarybutanol employed is in excess of the stoicliiometric amount required based on the rare earth salt.

7. The process of claim 6 wherein the ionizable rare earth salt is a trichloride of a rare earth metal.

8. The process of claim 7 wherein the rare earth metal is selected from the group consisting of yttrium and the elements having atomic numbers 57 through 71 inclusive.

9. The process of claim 8 wherein the rare earth metal is selected from the group consisting of yttrium, lanthanum, gadolinium and ytterbium.

10. The process of claim 9 wherein the ammonia is present as a gas and forms an atmosphere over the remainder of the reaction mixture.

References Cited UNITED STATES PATENTS 3,278,571 10/1966 Mazdiyasni et al. 260-429.2 3,419,610 12/1968 Temple 260-544 TOBIAS E. LEVOW, Primary Examiner A. P. DEMERS, Assistant Examiner OTHER REFERENCES Kapoor et al.: Chem. and Ind. (London), 1968, p. 1314.

US. Cl. X.R.

23204; 252-l3l N, 301.2 R; 260429.2 

